Fiber-reinforced ceramic brake linings

Abstract

A ceramic brake lining which is reinforced with carbon fibers and has a matrix which consists essentially of silicon carbide together with silicon and/or carbon, wherein the reinforcing fibers used are long fibers having a mean length of at least 10 mm which are aligned in the plane parallel to the friction surface, a process for its production and its use in combination with brake discs made of C/SiC or CFC or as lining in friction clutches.

1. A process for producing a brake lining which is reinforced with carbon fibers and has a matrix which consists essentially of silicon carbide together with silicon and/or carbon, wherein the reinforcing fibers used are long fibers having a mean length of at least 10 mm which are aligned in the plane parallel to the friction surface, which process comprises the following steps:
 a) production of a fiber arrangement of carbon fibers arranged essentially in a plane, wherein the fibers may be present in the form of individual fibers, fiber bundles or fiber yarns and the fibers and/or fiber bundles or fiber yarns being bound by a carbonizable binder, 
 b) shaping and/or curing of the bound fiber construction under pressure and/or at elevated temperature, if desired followed by further densification by means of carbonizable carbon precursors, 
 c) carbonization or graphitization of the bound cured fiber construction to produce a shaped body comprising carbon reinforced with carbon fibers (C/C), 
 d) at least one further densification of the C/C shaped body by means of pyrolytic carbon formed either by liquid-phase infiltration with carbonizable carbon precursors and subsequent carbonization or by gas-phase infiltration with carbon, and 
 e) infiltration of the densified C/C shaped body with a silicon melt and partial reaction of the silicon with at least part of the carbon in the shaped body to form silicon carbide, so as to give a composite ceramic comprising carbon fibers embedded in a matrix comprising SiC, Si and C (C/SiC) 
 
       such that the mass fraction of silicon in the material of the brake lining is at least 10%, and the mass fraction of silicon carbide is from 10% to 25%, and wherein the uppermost layer exposed to friction has a volume fraction of at least 50% of carbon fibres, and wherein the silicon content in the said friction layer is lower than the silicon carbide content in the said layer. 
     
     
       2. The process as claimed in  claim 1 , wherein the silicon melt in step e) further comprises additional metals selected from the group consisting of titanium, iron, chromium, copper and molybdenum. 
     
     
       3. A method of use of the brake lining obtained by the process of  claim 1  in combination with brake discs made of C/SiC, comprising arranging the brake linings in a caliper which extends around the flat surfaces of the brake disk. 
     
     
       4. A method of use of a brake lining as claimed in  claim 3  comprising fastening the brake lining on a metallic support, and combining the said brake lining on the said support with brake discs made of CFC to yield a brake system. 
     
     
       5. A method of use of a lining as obtained by the process of  claim 1  as friction lining in a friction clutch, comprising combining the said lining with a clutch disk.